Weight Distribution

Checking weight distribution

Checking the weight distribution

Weight distribution is one of the important aspects of suspension tuning as the car's weight distribution affects car handling, acceleration and traction. If a car's weight is not evenly distributed on the four tires, the traction on the tires will not be equal, and the handling characteristics will not be balanced, from left to right, making the car unpredictable when negotiating left and right hand corners. For good car handling it is important that the suspension is tuned so that the car's weight is distributed in the same proportion front-to-rear on the left and the right sides of the car.

You need to measure the weight on each wheel to determine the weight distribution but this must be done with the normal driving condition of the car, that is, with the driver in place and an average amount of fuel in the tank. You can measure the weight on each wheel by placing platform scales under the four tires. The scales must be of the same height to ensure that the car is level. If the car is not level then the readings from the scales will be inaccurate. Once you have the weight on the four tires, you can add them to find the total weight of the car.

Now you can determine the front-to-rear distribution of the car by adding the weight on the front tires and dividing that by the total weight of the car. This can be converted to a percentage by multiplying by 100 as follows:

percentage on front tires =  weight on left-front tire + weight on right-front tire
total weight of the car
 x 100

We can calculate the percentage of weight on the rear wheels in a similar manner:

percentage on rear tires =  weight on left-rear tire + weight on right-rear tire
total weight of the car
 x 100

The percentages on the front tires and the percentage on the rear tires should add up to 100% and will give you the front to rear weight distribution. Ideally, the front-to-rear weight distribution on the left side of the car should be the same as the front-to-rear weight distribution on the right side. In other words, if the front tires carry 60% of the total weight of the car, then the left-front tire should also carry 60% of the weight on the left side of the car, and the right-front tire should also carry 60% of the weight on the right side of the car.

Adjusting the Weight Distribution

You can adjust the weight on any one wheel by adjusting the ride height at that end of the car. For example, if you want to increase the weight at one wheel, you have to raise the ride height at that end of the car. However, when you adjust the weight at one wheel, the weight at the other three wheels is also affected and the weight needs to be redistributed. Therefore, if you want to adjust the weight at one wheel, you need to make a quarter of the adjustment at each wheel. Say, for example the front-left is 40 lb too heavy because of the driver, what you actually want to do is redistribute the weight equally by making the left-front 10 lb lighter and each of the other three corners 10 lb heavier. This means lowering the ride height on the left-front wheel until a decrease of 10 lb is reached, and raising the ride height on the right-front, left-rear, and right-rear wheels until the weight on each of those tires has increased by 10 lb.

With the weight distributed more equally, the car handling will be more predictable and the car will be easier to drive. However, changing the weight distribution also affects the car's center of gravity. In our next section we look at moving the car's center of gravity and the affect it has on the car's handling.